ORNL Lecture: Richard J. Weinberg, Part 3

FRIENDS OF OAK RIDGE NATIONAL LABORATORY LECTURE
Presentation by Richard Weinberg
Introduced by Dick Smyser and Alex Zucker
Donated by the American Museum of Science and Energy
April 2007
Transcribed by Jordan Reed
MR. SMYSER: First of all, folks, I'm Dick Smyser. I'm just going to open the program this evening. First of all, the rudimentary fire exit announcements. They’re here on the, my right, on my left and then the back and on either side also, in case we need to evacuate the hall.
Welcome to the third, the second of the fourth year of the Oak Ridge National, Friends of Oak Ridge National Laboratory Community Lectures. We have two more, well actually three more still coming because we have a “lucky strike extra”. How many people here know what a “lucky strike extra” is? Well, good. We have a “lucky strike extra” coming up on just a week from now, Thursday, May the 3rd. The details: it’s the Living History of Marie Curie. The details are all on the back of your program; I won’t go into them. Then actually the third of the established series will be on Wednesday, May the 23rd. Now, note that that is a day change. It has been moved back [ahead] one night because we found that we had conflict with the League of Women Voters candidate rally, which is going to be on Tuesday night, May the 22nd, and we didn’t want to conflict with that. So go to the candidate rally on the 22nd and then come here on the 23rd to hear Jane Weinshine [Joyce Maeinschein?]. And then on Tuesday, June the 19th, and note here there is another change. This lecture will begin an hour earlier at seven o’clock. It’s a lecture by Rom Uppuluri and the earlier starting time is to allow time for the presentation prior to the lecture of the Fourth Annual International Friendship Bell Award, which will be made in conjunction with that lecture. And now it is my pleasure to turn over the evening to the introducer of our speaker, Alex Zucker, who you all know as the former acting, associate and acting director of the Oak Ridge National Laboratory and currently a professor of physics at the University of Tennessee, Knoxville. Alex-
[Applause]
MR. ZUCKER: Well, it’s with great pride and pleasure that I introduce Richard Weinberg who will speak this evening. Pride because we are proud of our progeny. They contribute to the nation in the sciences, and the arts, in business and many other human endeavors and Dick is no exception. Pleasure because I knew Dick when he was in high school. When he was in high school, we used to go fencing together every Wednesday night for a couple of years. I drove him in my 1938 Chevrolet, which was a fairly famous car in its day and worked all the time. Well, as you can imagine, we had a number of conversations in that car because it didn’t go very fast, and I’ll come back to that in a few minutes. Dick graduated from high school and our driving in the Chevrolet stopped in 1964. It’s remarkable what he remembers about Oak Ridge. He remembers teachers. He remembers Ms. Laycock and Ms. Benson, who were math teachers, and I think his math seems to be in pretty good shape, and Mr. Pitts, who was from 8th grade, and Mr. Plumlee, who was a science teacher. He is clearly one of us. He is an Oak Ridge product and that is why I am proud of him. I have to do the obligatory pedigree. He got his BS in chemistry at the University of Chicago, and then he says he wanted to do something more, which I interpreted as being anything but chemistry. Someone then suggested physiology to him, and he said, “What is physiology?” And the answer from this person was, “Never mind, you’ll like it”. He got his Ph.D. in physiology from the University of Washington. Then he post-doced at the University of North Carolina in Charlotte in neuro-anatomy, and he has been there ever since. He’s professor of neuro-anatomy at the University of North Carolina. But there is a story here which involves Oak Ridge. When Dick was in college, he spent the summer in Oak Ridge with the MAN [Molecular Anatomy] Program. I don’t know how many of you remember it. It was run by Norman Anderson, who is in the mammalian anatomy program. Dick, I guess Norman lead him to an electron microscope and said, “This is where you will spend the summer”. So he spent the summer doing electron microscopy. At the end, Norman said, “You should really work on the central nervous system of insects”. I don’t know why he thought he had a gift for that, or maybe he thought the insects needed it. I don’t know, but anyway what he does now is not very far removed from that. Things are a little bigger, but a lot of it is neuro-anatomy using electron microscopes. Now, I also tried to influence Dick in a career, all those drives to and from fencing, and I had a somewhat different motivation. I tried to get him to do something that was as far removed from his father’s profession as possible. You know about sons and fathers- it’s a complicated relationship. In our ’38 Chevrolet, I thought I’d try to interest him in art history. (laughter) Well, it didn’t take, but I have to tell you why I did that, because there were, there was a very well-known physicist at that time by the name of Karnofsky, who was at Stanford, well, Berkley then Stanford, who did a lot of early work on mesons and so on. Very bright, very great physicist. He was known as the “Dumb” [David] Karnofsky. The “Smart” [Holden] Karnofsky was an art historian. I don’t know, but those who are into art history probably have seen his work and he is still regarded, the “Smart” Karnofsky, is still regarded as a giant in the field. So, I was thinking that maybe I could get Dick to be the “Smart” Weinberg, but… Well, that misfired. Well, anyway that is what I wished for Dick. He clearly decided not to take the advice from a guy who in the 1960’s was driving a 1938 Chevrolet. So, well, he went into physiology and it has really worked out for him. And so it’s a great pleasure for me to introduce Richard Weinberg, who will talk to us about glutamates, the brains favorite seasoning.
[Applause]
MR. WEINBERG: Thank you very much. Does the microphone work ok? No, it’s on. It’s ok. Everybody hear me. Good. Thank you, Alex for that nice introduction and thank you somewhat belatedly for [inaudible] rides in a ’38 Chevy. I also want to thank all of you for coming here tonight. I want to thank the Friends of ORNL [Oak Ridge National Laboratory] for inviting me. I particularly want to thank Fran Silver for all the work she did in arranging this. When I look at all the people in the audience, I have to say how sorry I am not to see one particular person in the audience. There was, Ernie Silver was a man that I knew quite well actually. I was a friend of his as well as a many of the people here. He was a man of remarkably broad learning and he, besides his knowledge of physics and many other things cultural and scientific, knew a surprising amount of about physiology and neuroscience. I actually had several relatively technical conversations with him about it. I am sorry that he couldn’t be here today. I wanted you to know that I miss him, too. Before I get into my talk, I want to also thank someone else that many of you know as a friend of ORNL and I know him also, not really as a friend of ORNL.
[Slide with picture of Alvin Weinberg and Richard’s daughter]
MR. WEINBERG: The point is that here we see my father instructing my daughter, and what you can see is that he’s got, first of all, there is a zest of enthusiasm in his expression. Second, as he details the fine points of Dabble Duck to my daughter, his immediate and intuitive grasp of the issues and her wrapped interest and spellbound way in which she attends to what he is saying. Well likewise, (Break in audio) …keeps fading… (Break in audio). Let me know if it goes dead again and I will deal with it when it does. Likewise at about this age, he explained… Should I just switch it? (Break in Audio) Testing, testing, 1, 2. Yeah. Bingo. People hear ok? Ok, thanks. Well, likewise he told me all about nuclear physics at about this age. So, I started off with an early interest in science.
[Slide with picture of yearbook page]
MR. WEINBERG: It developed through my training. Several of my classmates are here. This was Dwight Sullivan. This was Herbert Ork, I can’t see so well. And this is me at that point. Well, anyway, as Alex pointed out, I did finish and get out of here, finally, and now I am back after a long time.
[Slide with neuroscience info]
MR. WEINBERG: Today, I’m going to try to tell you a little bit about neuroscience. I had intended originally to say nothing about my work, just try to say something about neuroscience, but Alex told me, “No, that’s no good. You have to say something about your work.” So I will begin by saying a little about neuroscience. I will cover some basics, neurons and synapses, action potentials, synaptic potentials, and then I will get more into some specifics that are more closely related to work I do. I don’t mean in doing this to suggest that all of this is my invention by any means. I just want to use maybe my work as sort of a little local color to try to color in some of the trends that are growing on in neuroscience. It has become a big field. The last meeting of the Society for Neuroscience last year had 24,000 people in the audience, attendees and it’s sort of overwhelming now. But I will try to give you the big picture.
Science and other human disciplines can sort of be grouped in this category. Let’s say from general to specific, or elementary to composite, or simple to complicated. Likewise you can do that with scientific disciplines. I was brought up to believe that there was a hierarchy. Physics was the best, then you have the lesser people going into chemistry, and then marginally human into biology and then people that are beyond the pale. I am no longer persuaded of that, but what I have no doubt of is that chemistry builds on principles that are worked out and studied by physicists. Likewise biology builds on principles that are worked out and understood by chemists. But I don’t think it is accurate to suppose that a quantum chemist is prepared to explain how the heart beat works. And I don’t think likewise, I don’t question that without biology there would be no history, but I don’t think that any biologists are in the position to explain the causes of World War I. Well, within this same spectrum at a higher level of resolution, you can say you have cell biology which is sort of basic mechanisms of how cells work. Then you have neuroscience and then beyond that you have social science which is how human beings interact with each other, and within neuroscience you have a hierarchy, well not really a hierarchy, but a progression, cellular and systems neuroscience moving into psychology.
[Slide with flow chart]
MR. WEINBERG: My own research area is in cellular neuroscience. So that is mostly what I will be talking about today. Why study neuroscience? Well first of all, it’s interesting. It gets into some very profound questions that are not in any danger of being answered, having to do with what is thought? What is the relationship of mind and brain? Things of that kind, that people have worried about for a long time. I can assure you people will continue to worry about for a long time. If you hear anybody who says they have the answer, my suggestion is don’t look at them and just sort of keep walking. But it is an interesting field. It is one that is not likely to die from being answered too soon. In addition, it’s got very substantial and very real clinical significance. If you think about the progression of biology to neuroscience to social science, you can group a large number of the very serious misfortunes that happen to human beings in this spectrum. Ranging on the one hand from things such as stroke and brain tumor that certainly involve the brain. Certainly the study of neuroscience can help us to manage these or understand their pathology. But fundamentally, what is wrong in problems like that is something that is not within the sphere of neuroscience proper, but within the general sphere of the human organism. The same would be true if it was the liver or the heart, or anything else. Likewise on the other end, you have things like alcoholism or criminality. There is no question that our modern understanding of neuroscience has brought us to some clues, new insights into what might be going on. I think that the more crucial and central problems underlining these have more to do with interpersonal interactions and are perhaps more properly the realm of social science. Then there are things that are really pretty much central to neuroscience such as ALS [Amyotrophic Lateral Sclerosis] and Parkinson’s disease, perhaps schizophrenia, and then there are many, many other diseases. Many of these, I am afraid that you have heard of and many more that you haven’t heard of. I am afraid, it is a general and unhappy rule of thumb that if there is a neurologic disease that you haven’t heard of, that is not very good. I am also sorry to say that most of these are not now readily treatable, but we certainly have made progress in my lifetime in many of these. I think in particular that it may be before I die, that we see considerably more treatments for ALS and Parkinson’s disease, for example.
That is as much as I want to say about that. My work is not clinical. That is the human brain, which is a little more than 1 kilogram. This is the [front], where your face is. This is the back, and the anatomists in medical school learn all kinds of weird names for weird bumps and grooves. The frontal part of, this whole region is the cerebral cortex, a massively folded covering to the brain in humans and…
[Slide of brain diagram]
MR. WEINBERG: … it is thought to be the organ of thought. With moderate basis. In a very simple-minded way, you can think of this region as being concerned with movement and planning. This region back here is concerned with vision and visual understanding. This region is concerned with hearing, musical appreciation and the understanding of speech. There are other parts of the brain that, in humans, are covered by the cortex. This is the cerebellum, which coordinates movement. This region down here is called the brain stem which is the center for basic fundamental control of essential functions like blood pressure and respiration.
[slide with picture of nerves]
MR. WEINBERG: The brain is made up of nerve cells or neurons. The human brain has roughly 10 billion neurons in it. Neurons in some ways are like other cells and there are other ways they are very different. There are very many different kinds of neurons. It is tough to study them because the nervous system is packed with these suckers and each one of them has got all these things in it. So a technique called the “Golgi stain” was worked out a century ago. It stains individual neurons while leaving others unstained. Letting the scientists of the last century to work out the detailed structure of these cells. This is a characteristic cell in the cerebral cortex. This is the cell body, or soma. That is pretty much like the other cells of the body. It’s got a nucleus; it’s got ribosomes, mitochondria, the basic machinery that cells need to live. It’s where the DNA [Deoxyribonucleic acid] is. Then it’s got these funny processes that are absolutely typical of neurons and not of other things. These things are called dendrites and they radiate in characteristic ways different for different neurons. Then there is a long, long tube that comes off the bottom of a neuron, called an axon. And this is pretty stereotyped although the shapes are very different. It’s got a cell body, dendrites, and an axon. The cell body typically ranges from maybe to 10 to 50 micrometers in diameter, which is microscopic, but not very microscopic. If you have good vision, you can barely see something of the 100 micrometers in diameter. The dendrites are maybe a total of a couple of millimeters long, which is about this much. The axon can be very long. It can range from a couple millimeters to a couple of meters. Or one meter at least, so that there are neurons in your spinal cord that control your muscles in your foot. It uses an axon that is a meter long. On the dendrites, you can see, maybe, little tiny spiny things. Those are called dendritic spines. What happens is that the 10 billion neurons are all connected together. So the axon of one neuron goes to the dendrite of the next neuron where it sends messages. So you have this chain from this cell to this cell via the axon that is talking to this dendrite then this sends off an axon that goes to the next dendrite, or maybe it goes back. So on and so forth. I think you can imagine the potential complexity with 10 billion of these suckers. In addition, there may be, one of these cells may have 20 to 50 to 100 thousand contacts on it. So it’s got a lot of connections.
[Slide of scan from electron micrograph]
MR. WEINBERG: This is a scan from an electron micrograph of a nerve cell and culture. This is the cell body, the nucleus would be here and pretty much everything else you see is process, which is axons and dendrites, but mostly axons. This is a great oversimplification because this is a cell culture. This is two dimensions. The real brain is, thankfully, hopeless to get a decent image of, but maybe this gives you a sense of what we are talking about.
[Slide of drawing]
MR. WEINBERG: Ok, this artist conception gives you, maybe, a better feel for how things are in the brain. You have, here is a nerve cell. This is the cell body, the nucleus, and it’s just covered with these cute little guys that are called axonal boutons. These are coming from an axon, here is an axon, and it goes off here to these little swellings here. This is called a synapse, where the axons swelling touches the dendric swelling. That is the point of communication between one cell and the next.
[Slide of cell membrane]
MR. WEINBERG: Ok, so you have nerve cells that receive information. There are dendrites. They send information in their axons to the next cell, and the points of communications are called synapsis. I’m going to try to explain in five minutes how neurons work. This is going to be a little like one of those three minute presentations of Hamlet that some of the comedians do. So you’re going to get a three minute introduction into electrophysiology. This is the plasma membrane of a cell. All cells have pretty much the same plasma membrane. That is a membrane that surrounds the cell. It’s the boundary. It’s like the skin, but it’s for a cell. It’s made basically of a bi-layer of lipids, sort of like olive oil. As many of you know, lipids are very good electrical resisters. Transformers have oil in them because oil is a good electrical resister. In addition, they also have proteins. These things are proteins. Some of them are at the edge of the lipid and some are actually within the lipid, and these proteins play a very important role in the properties of nerve cells. They also play important roles in other cells.
[Slide of voltage ratings]
MR. WEINBERG: This is an experimental setup for studying the basic electrical properties of a neuron. This is a diagram of a neuron. You have, this is the microelectrode. It is a glass pipette that is pulled so tiny that the tip of it can actually go through the membrane of the cell without damaging the cell. It’s filled with a salt solution that conducts electricity and then you can actually put a voltmeter here that records the voltage. Then you have a second microelectrode that you are going to pass a current with. Those of you in the audience who know anything about electrical engineering will understand what I am going to say, clearly. The rest, I’m going to try to fake it. So what you can do is pass a test current into the cell and see how it responds with voltage. So what you’re doing is passing, hyperpolarizing current here, and depolarizing current here. Now, I should explain the zero is zero voltage and that all cells normally are not at zero voltage. There normally at about minus 60 millivolts. There is some variation depending on the kind of cell. The basis of that potential has to do with complicated things related to different ions. So, in any case, if you hyperpolarize a nerve cell, it hyperpolarizes in a funny pattern, characteristic of a linear capacitance circuit. If you depolarize it, you see the mirror image up to a certain point. This is all passive membrane properties related to the fact that lipids are resisters until a certain point, and then suddenly something completely different happens. You have a non-linear phenomenon. A sudden massive depolarization followed by a sudden repolarization. This so called spike, or action potential, is the mark of excitable tissue of a neuron. So, the spike, or action potential, is what makes, is one of the special features of nerve cells. That’s the message that a nerve cell uses when it’s talking from one nerve cell to the next.
[Slide: “Action potentials and synaptic potentials”]
[Slide with picture of a motor neuron]
MR. WEINBERG: I’m not very experienced at this high-tech computer stuff actually and it always gets me a little anxiety prone. Ok. This is a cartoon of a motor neuron in the spinal cord. It sits in the ventral horn of the spinal cord. This is the nucleus, cell body about 50 micrometers in diameter. These are dendrites; they extend for a couple millimeters. The dendrites are covered with synaptic boutons from axons that come from either the brain or within the spinal cord, making contacts there. Then it sends an axon out that is going to end up going to a muscle. This axon is covered with something called mylone, which is a fatty substance that covers, that acts as an electrical insulator. While I am thinking of it, that’s one of the things that goes wrong in the disease multiple sclerosis. The mylone sheath gets screwed up. But any way, so when an action potential happens in this motor neuron, the electrical disturbance propagates all the way down this axon, down to the next room, and the electrical signal goes to a muscle and tells that muscle to contract and it does contract and it goes fast. It gets there in maybe one or two milliseconds. What’s happening here is a little different.
[Slide with cartoon schematic]
MR. WEINBERG: This schematic cartoon of how neurons work. Here is the nerve cell. You have synapsis here. These are axons, axonal boutons. These appositions are called synapsis and you can either have an excitatory synapse, which causes a depolarization called an excitatory postsynaptic potential, or EPSP, or a hyper polarization, an inhibitory postsynaptic potential. An EPSP increases the chance that this nerve cell will fire an action potential. An IPSP will reduce the chance…
[End Video 1]
[Begin Video 2]
MR. WEINBERG: …that it will fire an action potential. All nerve cells in the brain have this constant play of excitation and inhibition. These are grated potentials, and then right here, these are decision making. It’s like the voting booth. You get the vote counted and then either it happens or it doesn’t happen. If it crosses a certain threshold, you get an action potential. And if you get the action potential, that’s it. End of story. The action potential in a stereotyped, very rapid way, gets propagated as an electrical disturbance down here to the output, where it then sends its message to the next neuron, and so on and so forth. And that’s how the brain works.
[Slide of magnified cell]
MR. WEINBERG: Any questions? [Laughter] Ok, good. Now this is a synapse at the electron micrograph, at the electron microscope. This is the mitochondria. This distance is about one micrometer. This is a presynaptic axonal bouton, one of those axonal swellings. This is the cell membrane, the plasma membrane bounding it. This is the dendritic spine that’s receiving a synapse. This area here is the synaptic specialization. This is the presynaptic active zone, synaptic cleft and extra cellular space that’s about 20 nanometers in distance. For reference, 20 nanometers is a little bit bigger than the average protein, and a lot smaller than a virus. Ok, this is the postsynaptic membrane and this thickening is called the postsynaptic density. So when you have an action potential here, it will trigger a synaptic potential here and what happens is that these little circles, or vesicles as they’re called, synaptic vesicles, are filled with special chemicals called neurotransmitters. And the action potential causes these vesicles to open up, go across the membrane, and somehow act on the postsynaptic side to do their stuff.
[Slide]
MR. WEINBERG: This was worked out in great detail. It’s still a subject of very active research, but the first person to make real progress was Sir Bernard Katz, who won a Nobel Prize in the late 1960’s for his work. The basic idea of it is that you have an action potential, a depolarization that depropagates very quickly down to the axon terminal. That causes, that voltage change in the membrane, causes these special proteins called calcium channels, voltage gated calcium channels, the protein changes its confirmation and goes from a closed state to an open state. When it’s open, these channels allow the ion calcium, which is at a fairly high concentration in the extra cellular space, and at very low concentration inside all normal living cells, allows the calcium to enter. Now calcium has all kinds of effects on enzymes. People are still actively involved in working out the details, but the bottom line is that calcium somehow triggers these vesicles to attach to the surface of the membrane and open up and spill their stuff out. So the transmitter goes into the membrane, I mean out of the membrane and into the extra cellular space where it touches these other guys called transmitter receptors, to then have a postsynaptic effect. Now receptors are something that all cells have. Receptors are something that used to be hypothetical constructs of pharmacologists. It turned out, has often turned out to be the case, notwithstanding my skepticism, pharmacologists had it right. Cells have receptors, all kinds of different receptors. I would guess that at least half the people in the audience are taking drugs now that act as receptors. Probably the most common of these are called beta blockers, which act as beta adrenergic receptors, but the drugs that work as antihistamines for allergies, drugs for headaches, drugs for pain, all kinds of drugs, work as receptors. But neurons have particularly specialized and developed receptors at the synapse.
[Slide: “Glutamate: The Natural Occurrence that was Discovered”]
MR. WEINBERG: When I was in graduate school, the identity of the main excitatory neurotransmitter was uncertain. People really didn’t know. But just about that time, they were talking. Well, maybe it’s glutamate. Now, glutamate is exactly the same stuff in Chinese food. My father told me I should really look this up and I found out, only this week to my surprise, that glutamate was actually first introduced as a seasoning in a purified form by the Japanese, not the Chinese. But it apparently, and not very long ago, 100 years ago, but it turns out they found it because there was a seaweed that had a lot of glutamate in it that was used as a traditional additive to stews. It turns out that many of the things used in western cooking in stews, such as meat stocks and certain kinds of vegetables, like tomatoes and mushrooms also have a lot of glutamate in them, and at least part of why they taste good is because they have a lot of glutamates. It adds a little zest to the food.
[Slide: “Is glutamate a neurotransmitter?”]
MR. WEINBERG: Well, is glutamate a neurotransmitter? The first reason people thought it might be is that glutamate excites neurons. If you squirt glutamate onto a neuron, which is not easy to do, but you can do it. It turns out to excite it. It causes action potentials. But it turned out that initial enthusiasm about this paled because people found that it excites all neurons. So it was thought, “Well, I guess it’s nothing special. It’s just some non-selective excitant, or toxicant, or something.” But then people said, “Ha, ha! Glutamate is only released by neurons when they are electrically active.” Now that’s very strong evidence indeed. But the trouble is those experiments are really, really tough. They are so tough that nobody was ever able to do it in a completely convincing way. So people were skeptics, didn’t really believe it. They didn’t have to. People found that there are pumps in neurons. In the membrane, remember I told you there are lots of proteins. Some of these pump from outside back in. You would expect if glutamate is a transmitter, that there should be pumps that take it back up. Sure enough there are pumps that take it back up. But it turns out, there are a hell of a lot of different pumps in neurons and in other cells, and they aren’t all related to neurotransmitters. In addition, glutamate is synthesized in neurons. There is the metabolic machinery to make glutamate, but it also turns out that glutamate is one of the key building blocks in all proteins, and that means all cells make glutamate. So that’s not too convincing either.
Well, some work that I was involved with was showing glutamate concentrates at synaptic terminals. And to explain how we did this…
[Slide: “Histochemistry”]
MR. WEINBERG: … I have to explain a little bit of background. There is a field that has been around for a while called histochemistry which is the study of chemicals in tissue, their localization in tissue. It’s a bit of a black art, but it’s been sort of specialized and in some ways made more general, and yet, more routine by the introduction of immunocytochemistry. Immunocytochemistry relies on the fact anything, you can make an antibody to anything. I mean, you can’t. A rabbit can’t, but if you do it right, if you treat a rabbit right, you can immunize them against anything. They, through their immune system, are able to make antibodies that are very specific in recognizing that chemical. This is a cartoon showing some chemical that you want to see that is in tissue. This is a cartoon of an immunoglobulin, an antibody that recognizes specifically this substance. Now the only trouble is that you can’t see an antibody, any better than the substance you want to see. But, ha, ha, what you can do is, before you add the antibody, you can do chemistry on it. You can do chemistry to add a tag that you can see. That’s what this little red thing is. Well, the tag can be a variety of things. Common examples include fluorescent dyes, enzymes, most commonly horseradish peroxidase, which is an enzyme which itself is invisible, but you can then add once it’s there, you can add a chemical that will react under the influence of horseradish peroxidase to make a colored dye substrate. So if this is horseradish peroxidase, then you add a brew of stuff to it, and it makes a whole lot of goop that fills up the area around here, and you can see it, either with a light microscope or an electron microscope. Or, you can have a small gold particle that will be too small to see with the light microscope, but you can see it as a little black dot at the electron microscopic level.
[Slide of axon terminal]
MR. WEINBERG: This is an axon terminal at the electron microscope. It’s in a part of the spinal cord that’s concerned with pain processing. And we know by its shape that it’s one of nerve terminals of a fiber that carries pain information. These are synapses of cells in the spinal cord. This is a neurotransmitter in little vesicles, and it’s black because it was reacted for an antibody to glutamate that was tagged with horseradish peroxidase, and then we did histochemistry on it to make that into an electron dense reaction product. This was evidence that, yes, these terminals are just filled with glutamate.
[Slide: “Glutamate Receptors”]
MR. WEINBERG: Ok, so that’s glutamate. Now what about glutamate receptors. We talked with glutamate as the presynaptic side, the axon bouton. What about the postsynaptic dendrite. Well, it turns out that after a lot of unsuccessful work, pharmacologists were finally able to make a variety of chemicals besides glutamate, that are sort of glutamate analogues that affect postsynaptic neurons in ways similar to glutamate. Two of these have the acronym AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-D-aspartate). I’m going to keep going back to AMPA and NMDA. Once they had these drugs, they were able to find other drugs called antagonists that would selectively block AMPA or selectively block NMDA. So if you had one of these AMPA antagonists, and you added AMPA, nothing happens. If you added NMDA antagonists, if you put an NMDA antagonist on and add NMDA, nothing happens. But if you put NMDA antagonists on and add AMPA, it works just fine. So they decided there must be NMDA and AMPA receptors.
[Slide]
MR. WEINBERG: Well, I thought they were silly, but what did I know. So, this is an electrical recording from a nerve cell. At its normal state of polarization, minus 60 millivolts, you stimulate a presynaptic axon that release glutamate and you get an excitatory potential called an EPSC [excitatory postsynaptic current]. Don’t worry about that. You put a special drug on that blocks NMDA receptors and what you get is this. And they say here is an AMPA component. You know it’s an AMPA component because if you then add to it a drug that blocks AMPA, this goes away and you get nothing. Contrariwise, here you have the same thing in EPSC. You put a drug on that blocks AMPA and your left with the NMDA component. So the whole thing is a combination of the NMDA and the AMPA component. The AMPA is fast. The NMDA is slower.
[Slide AMPA and NMDA diagrams]
MR. WEINBERG: In the last ten years, there have been a heck of a lot of work on this. They know a lot about these proteins now and there are good reasons for it. I’m not going to have time to tell you all of the reasons for it, but I’m going to hint at a few of the reasons. This is a diagram, a cartoon of an AMPA and NMDA receptor. This is the lipid by layer. This is inside. This is outside. This is where glutamate will be released and bind. This is glutamate binding to the receptor. When glutamate binds to the receptor that opens the channel, allowing current to flow which causes the EPSP [excitatory postsynaptic potential]. NMDA and AMPA, a little in particular, NMDA has more stuff in it, more things control it and regulate it, and it’s a little more complicated.
[Slide]
MR. WEINBERG: Well… Already? Gosh. Trouble, trouble, trouble. Ok, we wanted to know where these proteins were. Here we studied an AMPA receptor subunit using horseradish peroxidase. We were able to show that it was present in the dendrite, but that was about all we could say because the enzymatic reaction product diffuses some distance. You can’t get very good special resolution. This was using the same approach but using the immunogold label, which is much better localized. It’s these little black dots. So sure enough, the glutamate receptor is right at the postsynaptic membrane.
[Slide]
MR. WEINBERG: Now to look at this in a little more detail, this is the immunoglobulin that recognizes the substance. This is a gold particle. Because of the nature of the process, there is about a 20 nanometer range of possible error because where it ends up sitting down isn’t exactly where the sight of binding is. So there is maybe a little slop. Twenty nanometers is pretty good, but it’s not exact. So I had a post-doc, Victor Kerasia, who decided to take a look at this more systematically.
[Slide]
MR. WEINBERG: What he did was he just stained a lot of synapses in the cerebral cortex using immunogold for AMPA or NMDA subunits, and looked at where they were, and made a histogram of it. This is the distance to here. Ok. What he found was a spread, but that spread is about plus or minus 20 nanometers, which corresponds to the measurement error. So, if you don’t think about that measurement error, I mean if you try to correct for that and imagine what underlying distribution would give that, what you get is something that corresponds to right about here, which is just inside the plasma membrane. Ok. Just inside the plasma membrane. Moreover, though I don’t really claim that you can see it, the NMDA receptor is about two nanometers further than the AMPA receptor. That’s just barely statistically significant. Well, make sense? The answer is, ha, ha, it does.
[Slide]
MR. WEINBERG: This is a cartoon worked out by the molecular biologists of the protein organization of a subunit of an AMPA receptor. As all proteins, they are chains of amino acids. Amino acids have an N terminal and a C terminal. So a protein has an N terminal and a C terminal. Here is the N terminal. Here is the C terminal. This is outside. This is inside. Well, it turns out that the antibody that we were using recognizes the C terminal part of an AMPA receptor. So you would expect to see it just inside the membrane. And moreover, it turns out the NMDA receptor is organized just like the AMPA receptor except that it has a somewhat longer C terminus. So sure enough, you would expect to see it just a little bit further inside. So everything is as it should be.
[Slide: “Synaptic plasticity”]
MR. WEINBERG: And I have about three minutes to talk about the rest of the brain.
[Slide]
MR. WEINBERG: Let me zip through this and see if there is anything worth saying. Ok, the point is that besides the short transient phenomenon, there are also long term phenomenon that are important to the functioning of the brain. The fundamental thing to think about, although not the only example, is memory. While we don’t understand memory at any molecular level, an experimental tool that is being used recently that there has been great excitement over is synaptic plasticity. That is synapses can become more or less effective… Five minutes? Ok, yeah. And that’s been study particularly in the hippocampus, which is a region in this part of the brain that people know from different clinical and psychological studies, to be important for certain kinds of memory, particularly special memory. So when you get lost next time, you can just blame it on your hippocampus. Well, it turns out that you can actually cut a slice of hippocampus from the brain of a euthanatized rat and keep it alive for several hours in a petri dish…
[Slide]
MR. WEINBERG: …and that’s permitted very extensive study of this system, particularly this pathway, this synapse, where you stimulate the efferent fiber going to it and record from the nerve cell. This synapse releases glutamate, and the point to keep in mind here, is that if you stimulate once every five seconds, you get a certain synaptic potential, a certain amount of depolarization. It’s stable. It can be stable for hours, but if then, after you get a base line, 100 percent, you then deliver a rapid train of 100 stimuli over a period of a second, something changes. You get a whopping increase in the response. That increase settles down over five or ten minutes, but then it sticks around. It sticks around for an hour or more. If you do it right, it sticks around for a long time. You can’t keep these things alive in a dish forever, but there is good reason to think that you can do the same thing, pretty much, in a live animal and it will stay this way for weeks at least, if not forever. So people think that this might be one of the molecular, or one of the cellular substrates for things going on in memory.
[Slide]
MR. WEINBERG: Now what they think is happening is glutamate is being released all the time. Glutamate reacts at AMPA and NMDA receptors. But I tricked you. NMDA receptors, ha, ha, don’t normally work because they have magnesium ions in them that block its activity. It only unblocks when the thing is already depolarized by, for example, a train of stimuli that have activated AMPA receptors to cause a progressive depolarization. When this gets unblocked, the NMDA receptor starts working and allows a massive influx of calcium, and calcium, I told you at the beginning, acts on a whole bunch of different proteins, and these bunch of different proteins may cause biochemical changes that lead to long term reorganization of the synapse.
[Skips five slides]
MR. WEINBERG: This is a cartoon summarizing a lot of information from Eric Kandel’s textbook. He just won the Nobel Prize this year for pioneering work in synaptic plasticity in the hippocampus in an invertebrate. But it turns out there are mechanisms both operating on the postsynaptic side changing, for example, the concentration of postsynaptic receptors and mechanisms on the presynaptic side changing the efficacy of transmitter release.
[Skips slide]
MR. WEINBERG: I think I’ll have to stop there. I want to thank all my collaborators, the post-docs and students who have done the work for me, and my collaborators elsewhere. It sort of brings home to me one of the nice things about science, which is that you are sort of automatically part of a large community. What I’ve told you this evening is just a tiny little piece of this stuff that goes on with 25,000 people each year at the neuroscience meeting. And even if you took all of that stuff, you wouldn’t have a clue as to how the brain works because we don’t know how the brain works, but we are learning very, very slowly. Thank you for your time.
[Applause]
MR. WEINBERG: And I’ll take questions. Can we get the lights? So I’ll take questions from the audience now. No questions?
[Inaudible audience member]
MR. WEINBERG: Yeah. Neurons talk to each other. What do I mean by synaptic plasticity? What do I mean by synaptic plasticity? Neurons talk to each other via synapses. Ok, when an action potential, an action potential is completely stereotyped. When an action potential goes to a nerve terminal, the synapse turns on and you get a postsynaptic response. If you give 100 action potentials, you get 100 synaptic responses. Ordinarily, we think of that as stereotyped. The same action potential gives the same response, but it ain’t necessarily so. The synapse may become more effective. The synapse might become less effective. So they synapse has this property of plasticity. That is it changes for long periods of time to become more effective, or less effective.
[Inaudible audience member]
MR. WEINBERG: Normal magnetic fields, so far as people know, do things to the brain. It is possible… there are high tech methods that, I’m sure the people in the audience know better than I do, that can record magnetic fields in the brain as a result of the electrical activity of the neurons. There are some technical advantages to this although it requires very formidable machinery to do so. In addition to this, while a static magnetic field, as far as it is known, has no effect. A transient magnetic field induces I don’t know what, magnetic currents or something. Under the right circumstances that can actually stimulate a particular region of the brain causing various kinds of illusions, or so on, in an experimental subject.
[Inaudible audience member]
MR. WEINBERG: Yeah, the question is if understanding the brain is hopeless, what about neural nets? Can they tell us something about the brain? The short answer is yes, but first I need to qualify. We don’t understand the brain. We understand a little bit about the brain and we probably understand more each year. In my lifetime, there is no way we are going to understand what, to my mind, is a lot about the brain. Will we ever? I don’t know. Does modeling have something to tell us about how brains might work? Unquestionably, it does. At the same time, it has a bad reputation. It has a bad reputation because it promised too much too early. There were a lot of ambitious people who got excited about it. It’s understandably exciting. There was a divergence. What happened was that they got excited originally because they thought this might tell us how the brain works. Then it turned out they weren’t getting very far. They needed to keep the money flowing and they started to realize that if they weren’t getting very far in understanding how the brain works. They were doing pretty well in understanding how to use computers to do various useful kinds of things: language translations, or handling complicated problems with arranging scheduling for airlines, and things like that. So the electrical engineering field of neural networks has sort of taken on a very vital life of its own [inaudible] remains a very useful and important [inaudible] of realistic neural networks that have helped us to understand certain aspects of neural processing and will continue to in the future. But there is a limit to it. Some of the limit, again, is because it’s complicated. Some of it is sociological that, in fact, engineers and biologists [inaudible] each other as much as they should. Yeah.
AUDIENCE MEMBER: I wanted to ask you about something that confuses me very much.
MR. WEINBERG: Yes, sir.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
[Laughter]
MR. WEINBERG: Did I read his book? No. If I had read it, would I understand it? No. Is he a genius? Yes. Is he right? Probably to a very, very limited extent. He has, in my opinion…
[End Video 2]
[Begin Video 3]
MR. WEINBERG: …the problem that comes with being brilliant and winning a Nobel Prize, and that is it is hard to maintain perspective. So, I think he has something very important to say, but I think it’s not quite as important as he thinks, and I think he didn’t do a very good job of making it accessible. In the simple minded Mickey Mouse way that I understand it, it’s that neurons try different ways of understanding stuff, and there are a lot of neurons there. Ok, you got 10 billion neurons, each one has got 50,000 synapses, and they screw around with different stuff until they get something that sort of works. And if something sort of works, they go for it. Hey. At some level, that is probably true, but I don’t know why, but Francis Crick, who by rights should be accused of exactly the same, is exposed to exactly the same mediology as [inaudible] namely being a genius and winning a Nobel Prize, seems to have a much more feet-on-the-ground attitude about it. My speculation is that maybe [Gerald] Edelman, I think got his prize in biology and so he supposed that he already understood it. Whereas Crick, well Crick got his in biology, but he was a physicist, alright. So he must of on some level known he didn’t know what was going on. But I don’t know.
[Inaudible audience member]
MR. WEINBERG: Ok, there was a question back there.
AUDIENCE MEMBER: You mentioned that glutamate rich foods are mushrooms and tomatoes.
MR. WEINBERG: I’m not sure. I think so. Tomatoes I’m sure.
AUDIENCE MEMBER: They have always made me feel better. [Laughter] Should I continue having, keeping them on my diet?
MR. WEINBERG: I strongly recommend that you eat what makes you feel good. [Laughter] I’m sorry. Let me make an addition. Two principles of eating: eat what makes you feel good, and eat what tastes good. [Laughter]
AUDIENCE MEMBER: This is back to the question on synaptic plasticity.
MR. WEINBERG: Yeah.
AUDIENCE MEMBER: You made reference to changing magnetic fields…
MR. WEINBERG: Yeah.
AUDIENCE MEMBER: …along synaptic activity, or presumably alluding to the effect of hallucinations in some subjects. Has there been any speculation or study with regard to conceivably, as small as this is. Is there a change at the synaptic junction when there is movement, electrochemical movement, either through the neurons or across, particularly though the synaptic junction. Would it not be conceivable that there is coincident with that a brief magnetic field generated, which in turn could affect other synaptic processes? I don’t know how one would map something like this, but it seems like depending on the nature and the direction of the synaptic movement, this could in turn affect, you know, how other synapses are functioning. Has anyone looked into that at this point?
MR. WEINBERG: Ok, I can’t give a whole and full answer to that. I can give a sort of talk around it. One, there has been a lot of excitement about the possibility of electromagnetic fields doing something bad to the body. I don’t think anybody, today, really knows. But the bulk of the available, the bulk of the available epidemiological research today argues that its very little of a problem, if any, that might also possibly effect the brain, thought processes and so on. So far as I know, there is no evidence to support it, although it can’t be ruled out. Now, you’re talking more about another thing, I think, which is sort of direct electrical, electromagnetic influences from one neuron to another. If you take the non-crack component of ESP, of let’s say telepathy, I think that the people who have taken it seriously in the past, who were saying maybe you really can transmit thoughts, one of the things they considered was the possibility that there might be some kind of electromagnetic emanation. I think that there is a lot of reason to think that is not true. The biggest reason has to do with sort of physical arguments having to do with arguments of scale that just impress most people with the very implausible. I don’t think that the implausibility arguments, I think they are pretty good with ESP, but I don’t think they are so good with respect to one part of the brain versus a different part of the brain. Because what physicists don’t realize is that there are biological systems that are capable of detecting extraordinarily slight electric fields. Biological systems can make sensors that are about as good as physical sensors, but I guess what I would say is that, at this point, the general view is that it doesn’t amount to much. Yes, sir.
[Inaudible audience member]
MR. WEINBERG: That’s a big number. So if there is an effect, it will be an electromagnetic effect.
[Inaudible audience member]
MR. WEINBERG: Ok.
[Inaudible audience member]
MR. WEINBERG: Ok, so I was too harsh on Edelman. [Laughter] And I agree with you. I think that there is something incredibly irresponsible in my bad rapping some guy when I haven’t even had the time to sit down and read his book carefully. I’ve had some people that I respect tell me that he is really onto something. What I’m personally convinced of is that whether he is on to something or not, it’s not on “the key” to understanding the brain. And that I’ll bet on, whether he’s right or not about his neuro-Darwinism.
[Inaudible audience member]
MR. WEINBERG: I don’t… That’s exactly why I’ll bet on it because I don’t think there is a key. Maybe we should stop now and if people want to continue to ask questions I’ll stay here and answer questions until the cows come home, but why don’t we stop and let people who need to get home, go.
[Applause]
MR. WEINBERG: Thank you very much.
[End of Lecture]

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FRIENDS OF OAK RIDGE NATIONAL LABORATORY LECTURE
Presentation by Richard Weinberg
Introduced by Dick Smyser and Alex Zucker
Donated by the American Museum of Science and Energy
April 2007
Transcribed by Jordan Reed
MR. SMYSER: First of all, folks, I'm Dick Smyser. I'm just going to open the program this evening. First of all, the rudimentary fire exit announcements. They’re here on the, my right, on my left and then the back and on either side also, in case we need to evacuate the hall.
Welcome to the third, the second of the fourth year of the Oak Ridge National, Friends of Oak Ridge National Laboratory Community Lectures. We have two more, well actually three more still coming because we have a “lucky strike extra”. How many people here know what a “lucky strike extra” is? Well, good. We have a “lucky strike extra” coming up on just a week from now, Thursday, May the 3rd. The details: it’s the Living History of Marie Curie. The details are all on the back of your program; I won’t go into them. Then actually the third of the established series will be on Wednesday, May the 23rd. Now, note that that is a day change. It has been moved back [ahead] one night because we found that we had conflict with the League of Women Voters candidate rally, which is going to be on Tuesday night, May the 22nd, and we didn’t want to conflict with that. So go to the candidate rally on the 22nd and then come here on the 23rd to hear Jane Weinshine [Joyce Maeinschein?]. And then on Tuesday, June the 19th, and note here there is another change. This lecture will begin an hour earlier at seven o’clock. It’s a lecture by Rom Uppuluri and the earlier starting time is to allow time for the presentation prior to the lecture of the Fourth Annual International Friendship Bell Award, which will be made in conjunction with that lecture. And now it is my pleasure to turn over the evening to the introducer of our speaker, Alex Zucker, who you all know as the former acting, associate and acting director of the Oak Ridge National Laboratory and currently a professor of physics at the University of Tennessee, Knoxville. Alex-
[Applause]
MR. ZUCKER: Well, it’s with great pride and pleasure that I introduce Richard Weinberg who will speak this evening. Pride because we are proud of our progeny. They contribute to the nation in the sciences, and the arts, in business and many other human endeavors and Dick is no exception. Pleasure because I knew Dick when he was in high school. When he was in high school, we used to go fencing together every Wednesday night for a couple of years. I drove him in my 1938 Chevrolet, which was a fairly famous car in its day and worked all the time. Well, as you can imagine, we had a number of conversations in that car because it didn’t go very fast, and I’ll come back to that in a few minutes. Dick graduated from high school and our driving in the Chevrolet stopped in 1964. It’s remarkable what he remembers about Oak Ridge. He remembers teachers. He remembers Ms. Laycock and Ms. Benson, who were math teachers, and I think his math seems to be in pretty good shape, and Mr. Pitts, who was from 8th grade, and Mr. Plumlee, who was a science teacher. He is clearly one of us. He is an Oak Ridge product and that is why I am proud of him. I have to do the obligatory pedigree. He got his BS in chemistry at the University of Chicago, and then he says he wanted to do something more, which I interpreted as being anything but chemistry. Someone then suggested physiology to him, and he said, “What is physiology?” And the answer from this person was, “Never mind, you’ll like it”. He got his Ph.D. in physiology from the University of Washington. Then he post-doced at the University of North Carolina in Charlotte in neuro-anatomy, and he has been there ever since. He’s professor of neuro-anatomy at the University of North Carolina. But there is a story here which involves Oak Ridge. When Dick was in college, he spent the summer in Oak Ridge with the MAN [Molecular Anatomy] Program. I don’t know how many of you remember it. It was run by Norman Anderson, who is in the mammalian anatomy program. Dick, I guess Norman lead him to an electron microscope and said, “This is where you will spend the summer”. So he spent the summer doing electron microscopy. At the end, Norman said, “You should really work on the central nervous system of insects”. I don’t know why he thought he had a gift for that, or maybe he thought the insects needed it. I don’t know, but anyway what he does now is not very far removed from that. Things are a little bigger, but a lot of it is neuro-anatomy using electron microscopes. Now, I also tried to influence Dick in a career, all those drives to and from fencing, and I had a somewhat different motivation. I tried to get him to do something that was as far removed from his father’s profession as possible. You know about sons and fathers- it’s a complicated relationship. In our ’38 Chevrolet, I thought I’d try to interest him in art history. (laughter) Well, it didn’t take, but I have to tell you why I did that, because there were, there was a very well-known physicist at that time by the name of Karnofsky, who was at Stanford, well, Berkley then Stanford, who did a lot of early work on mesons and so on. Very bright, very great physicist. He was known as the “Dumb” [David] Karnofsky. The “Smart” [Holden] Karnofsky was an art historian. I don’t know, but those who are into art history probably have seen his work and he is still regarded, the “Smart” Karnofsky, is still regarded as a giant in the field. So, I was thinking that maybe I could get Dick to be the “Smart” Weinberg, but… Well, that misfired. Well, anyway that is what I wished for Dick. He clearly decided not to take the advice from a guy who in the 1960’s was driving a 1938 Chevrolet. So, well, he went into physiology and it has really worked out for him. And so it’s a great pleasure for me to introduce Richard Weinberg, who will talk to us about glutamates, the brains favorite seasoning.
[Applause]
MR. WEINBERG: Thank you very much. Does the microphone work ok? No, it’s on. It’s ok. Everybody hear me. Good. Thank you, Alex for that nice introduction and thank you somewhat belatedly for [inaudible] rides in a ’38 Chevy. I also want to thank all of you for coming here tonight. I want to thank the Friends of ORNL [Oak Ridge National Laboratory] for inviting me. I particularly want to thank Fran Silver for all the work she did in arranging this. When I look at all the people in the audience, I have to say how sorry I am not to see one particular person in the audience. There was, Ernie Silver was a man that I knew quite well actually. I was a friend of his as well as a many of the people here. He was a man of remarkably broad learning and he, besides his knowledge of physics and many other things cultural and scientific, knew a surprising amount of about physiology and neuroscience. I actually had several relatively technical conversations with him about it. I am sorry that he couldn’t be here today. I wanted you to know that I miss him, too. Before I get into my talk, I want to also thank someone else that many of you know as a friend of ORNL and I know him also, not really as a friend of ORNL.
[Slide with picture of Alvin Weinberg and Richard’s daughter]
MR. WEINBERG: The point is that here we see my father instructing my daughter, and what you can see is that he’s got, first of all, there is a zest of enthusiasm in his expression. Second, as he details the fine points of Dabble Duck to my daughter, his immediate and intuitive grasp of the issues and her wrapped interest and spellbound way in which she attends to what he is saying. Well likewise, (Break in audio) …keeps fading… (Break in audio). Let me know if it goes dead again and I will deal with it when it does. Likewise at about this age, he explained… Should I just switch it? (Break in Audio) Testing, testing, 1, 2. Yeah. Bingo. People hear ok? Ok, thanks. Well, likewise he told me all about nuclear physics at about this age. So, I started off with an early interest in science.
[Slide with picture of yearbook page]
MR. WEINBERG: It developed through my training. Several of my classmates are here. This was Dwight Sullivan. This was Herbert Ork, I can’t see so well. And this is me at that point. Well, anyway, as Alex pointed out, I did finish and get out of here, finally, and now I am back after a long time.
[Slide with neuroscience info]
MR. WEINBERG: Today, I’m going to try to tell you a little bit about neuroscience. I had intended originally to say nothing about my work, just try to say something about neuroscience, but Alex told me, “No, that’s no good. You have to say something about your work.” So I will begin by saying a little about neuroscience. I will cover some basics, neurons and synapses, action potentials, synaptic potentials, and then I will get more into some specifics that are more closely related to work I do. I don’t mean in doing this to suggest that all of this is my invention by any means. I just want to use maybe my work as sort of a little local color to try to color in some of the trends that are growing on in neuroscience. It has become a big field. The last meeting of the Society for Neuroscience last year had 24,000 people in the audience, attendees and it’s sort of overwhelming now. But I will try to give you the big picture.
Science and other human disciplines can sort of be grouped in this category. Let’s say from general to specific, or elementary to composite, or simple to complicated. Likewise you can do that with scientific disciplines. I was brought up to believe that there was a hierarchy. Physics was the best, then you have the lesser people going into chemistry, and then marginally human into biology and then people that are beyond the pale. I am no longer persuaded of that, but what I have no doubt of is that chemistry builds on principles that are worked out and studied by physicists. Likewise biology builds on principles that are worked out and understood by chemists. But I don’t think it is accurate to suppose that a quantum chemist is prepared to explain how the heart beat works. And I don’t think likewise, I don’t question that without biology there would be no history, but I don’t think that any biologists are in the position to explain the causes of World War I. Well, within this same spectrum at a higher level of resolution, you can say you have cell biology which is sort of basic mechanisms of how cells work. Then you have neuroscience and then beyond that you have social science which is how human beings interact with each other, and within neuroscience you have a hierarchy, well not really a hierarchy, but a progression, cellular and systems neuroscience moving into psychology.
[Slide with flow chart]
MR. WEINBERG: My own research area is in cellular neuroscience. So that is mostly what I will be talking about today. Why study neuroscience? Well first of all, it’s interesting. It gets into some very profound questions that are not in any danger of being answered, having to do with what is thought? What is the relationship of mind and brain? Things of that kind, that people have worried about for a long time. I can assure you people will continue to worry about for a long time. If you hear anybody who says they have the answer, my suggestion is don’t look at them and just sort of keep walking. But it is an interesting field. It is one that is not likely to die from being answered too soon. In addition, it’s got very substantial and very real clinical significance. If you think about the progression of biology to neuroscience to social science, you can group a large number of the very serious misfortunes that happen to human beings in this spectrum. Ranging on the one hand from things such as stroke and brain tumor that certainly involve the brain. Certainly the study of neuroscience can help us to manage these or understand their pathology. But fundamentally, what is wrong in problems like that is something that is not within the sphere of neuroscience proper, but within the general sphere of the human organism. The same would be true if it was the liver or the heart, or anything else. Likewise on the other end, you have things like alcoholism or criminality. There is no question that our modern understanding of neuroscience has brought us to some clues, new insights into what might be going on. I think that the more crucial and central problems underlining these have more to do with interpersonal interactions and are perhaps more properly the realm of social science. Then there are things that are really pretty much central to neuroscience such as ALS [Amyotrophic Lateral Sclerosis] and Parkinson’s disease, perhaps schizophrenia, and then there are many, many other diseases. Many of these, I am afraid that you have heard of and many more that you haven’t heard of. I am afraid, it is a general and unhappy rule of thumb that if there is a neurologic disease that you haven’t heard of, that is not very good. I am also sorry to say that most of these are not now readily treatable, but we certainly have made progress in my lifetime in many of these. I think in particular that it may be before I die, that we see considerably more treatments for ALS and Parkinson’s disease, for example.
That is as much as I want to say about that. My work is not clinical. That is the human brain, which is a little more than 1 kilogram. This is the [front], where your face is. This is the back, and the anatomists in medical school learn all kinds of weird names for weird bumps and grooves. The frontal part of, this whole region is the cerebral cortex, a massively folded covering to the brain in humans and…
[Slide of brain diagram]
MR. WEINBERG: … it is thought to be the organ of thought. With moderate basis. In a very simple-minded way, you can think of this region as being concerned with movement and planning. This region back here is concerned with vision and visual understanding. This region is concerned with hearing, musical appreciation and the understanding of speech. There are other parts of the brain that, in humans, are covered by the cortex. This is the cerebellum, which coordinates movement. This region down here is called the brain stem which is the center for basic fundamental control of essential functions like blood pressure and respiration.
[slide with picture of nerves]
MR. WEINBERG: The brain is made up of nerve cells or neurons. The human brain has roughly 10 billion neurons in it. Neurons in some ways are like other cells and there are other ways they are very different. There are very many different kinds of neurons. It is tough to study them because the nervous system is packed with these suckers and each one of them has got all these things in it. So a technique called the “Golgi stain” was worked out a century ago. It stains individual neurons while leaving others unstained. Letting the scientists of the last century to work out the detailed structure of these cells. This is a characteristic cell in the cerebral cortex. This is the cell body, or soma. That is pretty much like the other cells of the body. It’s got a nucleus; it’s got ribosomes, mitochondria, the basic machinery that cells need to live. It’s where the DNA [Deoxyribonucleic acid] is. Then it’s got these funny processes that are absolutely typical of neurons and not of other things. These things are called dendrites and they radiate in characteristic ways different for different neurons. Then there is a long, long tube that comes off the bottom of a neuron, called an axon. And this is pretty stereotyped although the shapes are very different. It’s got a cell body, dendrites, and an axon. The cell body typically ranges from maybe to 10 to 50 micrometers in diameter, which is microscopic, but not very microscopic. If you have good vision, you can barely see something of the 100 micrometers in diameter. The dendrites are maybe a total of a couple of millimeters long, which is about this much. The axon can be very long. It can range from a couple millimeters to a couple of meters. Or one meter at least, so that there are neurons in your spinal cord that control your muscles in your foot. It uses an axon that is a meter long. On the dendrites, you can see, maybe, little tiny spiny things. Those are called dendritic spines. What happens is that the 10 billion neurons are all connected together. So the axon of one neuron goes to the dendrite of the next neuron where it sends messages. So you have this chain from this cell to this cell via the axon that is talking to this dendrite then this sends off an axon that goes to the next dendrite, or maybe it goes back. So on and so forth. I think you can imagine the potential complexity with 10 billion of these suckers. In addition, there may be, one of these cells may have 20 to 50 to 100 thousand contacts on it. So it’s got a lot of connections.
[Slide of scan from electron micrograph]
MR. WEINBERG: This is a scan from an electron micrograph of a nerve cell and culture. This is the cell body, the nucleus would be here and pretty much everything else you see is process, which is axons and dendrites, but mostly axons. This is a great oversimplification because this is a cell culture. This is two dimensions. The real brain is, thankfully, hopeless to get a decent image of, but maybe this gives you a sense of what we are talking about.
[Slide of drawing]
MR. WEINBERG: Ok, this artist conception gives you, maybe, a better feel for how things are in the brain. You have, here is a nerve cell. This is the cell body, the nucleus, and it’s just covered with these cute little guys that are called axonal boutons. These are coming from an axon, here is an axon, and it goes off here to these little swellings here. This is called a synapse, where the axons swelling touches the dendric swelling. That is the point of communication between one cell and the next.
[Slide of cell membrane]
MR. WEINBERG: Ok, so you have nerve cells that receive information. There are dendrites. They send information in their axons to the next cell, and the points of communications are called synapsis. I’m going to try to explain in five minutes how neurons work. This is going to be a little like one of those three minute presentations of Hamlet that some of the comedians do. So you’re going to get a three minute introduction into electrophysiology. This is the plasma membrane of a cell. All cells have pretty much the same plasma membrane. That is a membrane that surrounds the cell. It’s the boundary. It’s like the skin, but it’s for a cell. It’s made basically of a bi-layer of lipids, sort of like olive oil. As many of you know, lipids are very good electrical resisters. Transformers have oil in them because oil is a good electrical resister. In addition, they also have proteins. These things are proteins. Some of them are at the edge of the lipid and some are actually within the lipid, and these proteins play a very important role in the properties of nerve cells. They also play important roles in other cells.
[Slide of voltage ratings]
MR. WEINBERG: This is an experimental setup for studying the basic electrical properties of a neuron. This is a diagram of a neuron. You have, this is the microelectrode. It is a glass pipette that is pulled so tiny that the tip of it can actually go through the membrane of the cell without damaging the cell. It’s filled with a salt solution that conducts electricity and then you can actually put a voltmeter here that records the voltage. Then you have a second microelectrode that you are going to pass a current with. Those of you in the audience who know anything about electrical engineering will understand what I am going to say, clearly. The rest, I’m going to try to fake it. So what you can do is pass a test current into the cell and see how it responds with voltage. So what you’re doing is passing, hyperpolarizing current here, and depolarizing current here. Now, I should explain the zero is zero voltage and that all cells normally are not at zero voltage. There normally at about minus 60 millivolts. There is some variation depending on the kind of cell. The basis of that potential has to do with complicated things related to different ions. So, in any case, if you hyperpolarize a nerve cell, it hyperpolarizes in a funny pattern, characteristic of a linear capacitance circuit. If you depolarize it, you see the mirror image up to a certain point. This is all passive membrane properties related to the fact that lipids are resisters until a certain point, and then suddenly something completely different happens. You have a non-linear phenomenon. A sudden massive depolarization followed by a sudden repolarization. This so called spike, or action potential, is the mark of excitable tissue of a neuron. So, the spike, or action potential, is what makes, is one of the special features of nerve cells. That’s the message that a nerve cell uses when it’s talking from one nerve cell to the next.
[Slide: “Action potentials and synaptic potentials”]
[Slide with picture of a motor neuron]
MR. WEINBERG: I’m not very experienced at this high-tech computer stuff actually and it always gets me a little anxiety prone. Ok. This is a cartoon of a motor neuron in the spinal cord. It sits in the ventral horn of the spinal cord. This is the nucleus, cell body about 50 micrometers in diameter. These are dendrites; they extend for a couple millimeters. The dendrites are covered with synaptic boutons from axons that come from either the brain or within the spinal cord, making contacts there. Then it sends an axon out that is going to end up going to a muscle. This axon is covered with something called mylone, which is a fatty substance that covers, that acts as an electrical insulator. While I am thinking of it, that’s one of the things that goes wrong in the disease multiple sclerosis. The mylone sheath gets screwed up. But any way, so when an action potential happens in this motor neuron, the electrical disturbance propagates all the way down this axon, down to the next room, and the electrical signal goes to a muscle and tells that muscle to contract and it does contract and it goes fast. It gets there in maybe one or two milliseconds. What’s happening here is a little different.
[Slide with cartoon schematic]
MR. WEINBERG: This schematic cartoon of how neurons work. Here is the nerve cell. You have synapsis here. These are axons, axonal boutons. These appositions are called synapsis and you can either have an excitatory synapse, which causes a depolarization called an excitatory postsynaptic potential, or EPSP, or a hyper polarization, an inhibitory postsynaptic potential. An EPSP increases the chance that this nerve cell will fire an action potential. An IPSP will reduce the chance…
[End Video 1]
[Begin Video 2]
MR. WEINBERG: …that it will fire an action potential. All nerve cells in the brain have this constant play of excitation and inhibition. These are grated potentials, and then right here, these are decision making. It’s like the voting booth. You get the vote counted and then either it happens or it doesn’t happen. If it crosses a certain threshold, you get an action potential. And if you get the action potential, that’s it. End of story. The action potential in a stereotyped, very rapid way, gets propagated as an electrical disturbance down here to the output, where it then sends its message to the next neuron, and so on and so forth. And that’s how the brain works.
[Slide of magnified cell]
MR. WEINBERG: Any questions? [Laughter] Ok, good. Now this is a synapse at the electron micrograph, at the electron microscope. This is the mitochondria. This distance is about one micrometer. This is a presynaptic axonal bouton, one of those axonal swellings. This is the cell membrane, the plasma membrane bounding it. This is the dendritic spine that’s receiving a synapse. This area here is the synaptic specialization. This is the presynaptic active zone, synaptic cleft and extra cellular space that’s about 20 nanometers in distance. For reference, 20 nanometers is a little bit bigger than the average protein, and a lot smaller than a virus. Ok, this is the postsynaptic membrane and this thickening is called the postsynaptic density. So when you have an action potential here, it will trigger a synaptic potential here and what happens is that these little circles, or vesicles as they’re called, synaptic vesicles, are filled with special chemicals called neurotransmitters. And the action potential causes these vesicles to open up, go across the membrane, and somehow act on the postsynaptic side to do their stuff.
[Slide]
MR. WEINBERG: This was worked out in great detail. It’s still a subject of very active research, but the first person to make real progress was Sir Bernard Katz, who won a Nobel Prize in the late 1960’s for his work. The basic idea of it is that you have an action potential, a depolarization that depropagates very quickly down to the axon terminal. That causes, that voltage change in the membrane, causes these special proteins called calcium channels, voltage gated calcium channels, the protein changes its confirmation and goes from a closed state to an open state. When it’s open, these channels allow the ion calcium, which is at a fairly high concentration in the extra cellular space, and at very low concentration inside all normal living cells, allows the calcium to enter. Now calcium has all kinds of effects on enzymes. People are still actively involved in working out the details, but the bottom line is that calcium somehow triggers these vesicles to attach to the surface of the membrane and open up and spill their stuff out. So the transmitter goes into the membrane, I mean out of the membrane and into the extra cellular space where it touches these other guys called transmitter receptors, to then have a postsynaptic effect. Now receptors are something that all cells have. Receptors are something that used to be hypothetical constructs of pharmacologists. It turned out, has often turned out to be the case, notwithstanding my skepticism, pharmacologists had it right. Cells have receptors, all kinds of different receptors. I would guess that at least half the people in the audience are taking drugs now that act as receptors. Probably the most common of these are called beta blockers, which act as beta adrenergic receptors, but the drugs that work as antihistamines for allergies, drugs for headaches, drugs for pain, all kinds of drugs, work as receptors. But neurons have particularly specialized and developed receptors at the synapse.
[Slide: “Glutamate: The Natural Occurrence that was Discovered”]
MR. WEINBERG: When I was in graduate school, the identity of the main excitatory neurotransmitter was uncertain. People really didn’t know. But just about that time, they were talking. Well, maybe it’s glutamate. Now, glutamate is exactly the same stuff in Chinese food. My father told me I should really look this up and I found out, only this week to my surprise, that glutamate was actually first introduced as a seasoning in a purified form by the Japanese, not the Chinese. But it apparently, and not very long ago, 100 years ago, but it turns out they found it because there was a seaweed that had a lot of glutamate in it that was used as a traditional additive to stews. It turns out that many of the things used in western cooking in stews, such as meat stocks and certain kinds of vegetables, like tomatoes and mushrooms also have a lot of glutamate in them, and at least part of why they taste good is because they have a lot of glutamates. It adds a little zest to the food.
[Slide: “Is glutamate a neurotransmitter?”]
MR. WEINBERG: Well, is glutamate a neurotransmitter? The first reason people thought it might be is that glutamate excites neurons. If you squirt glutamate onto a neuron, which is not easy to do, but you can do it. It turns out to excite it. It causes action potentials. But it turned out that initial enthusiasm about this paled because people found that it excites all neurons. So it was thought, “Well, I guess it’s nothing special. It’s just some non-selective excitant, or toxicant, or something.” But then people said, “Ha, ha! Glutamate is only released by neurons when they are electrically active.” Now that’s very strong evidence indeed. But the trouble is those experiments are really, really tough. They are so tough that nobody was ever able to do it in a completely convincing way. So people were skeptics, didn’t really believe it. They didn’t have to. People found that there are pumps in neurons. In the membrane, remember I told you there are lots of proteins. Some of these pump from outside back in. You would expect if glutamate is a transmitter, that there should be pumps that take it back up. Sure enough there are pumps that take it back up. But it turns out, there are a hell of a lot of different pumps in neurons and in other cells, and they aren’t all related to neurotransmitters. In addition, glutamate is synthesized in neurons. There is the metabolic machinery to make glutamate, but it also turns out that glutamate is one of the key building blocks in all proteins, and that means all cells make glutamate. So that’s not too convincing either.
Well, some work that I was involved with was showing glutamate concentrates at synaptic terminals. And to explain how we did this…
[Slide: “Histochemistry”]
MR. WEINBERG: … I have to explain a little bit of background. There is a field that has been around for a while called histochemistry which is the study of chemicals in tissue, their localization in tissue. It’s a bit of a black art, but it’s been sort of specialized and in some ways made more general, and yet, more routine by the introduction of immunocytochemistry. Immunocytochemistry relies on the fact anything, you can make an antibody to anything. I mean, you can’t. A rabbit can’t, but if you do it right, if you treat a rabbit right, you can immunize them against anything. They, through their immune system, are able to make antibodies that are very specific in recognizing that chemical. This is a cartoon showing some chemical that you want to see that is in tissue. This is a cartoon of an immunoglobulin, an antibody that recognizes specifically this substance. Now the only trouble is that you can’t see an antibody, any better than the substance you want to see. But, ha, ha, what you can do is, before you add the antibody, you can do chemistry on it. You can do chemistry to add a tag that you can see. That’s what this little red thing is. Well, the tag can be a variety of things. Common examples include fluorescent dyes, enzymes, most commonly horseradish peroxidase, which is an enzyme which itself is invisible, but you can then add once it’s there, you can add a chemical that will react under the influence of horseradish peroxidase to make a colored dye substrate. So if this is horseradish peroxidase, then you add a brew of stuff to it, and it makes a whole lot of goop that fills up the area around here, and you can see it, either with a light microscope or an electron microscope. Or, you can have a small gold particle that will be too small to see with the light microscope, but you can see it as a little black dot at the electron microscopic level.
[Slide of axon terminal]
MR. WEINBERG: This is an axon terminal at the electron microscope. It’s in a part of the spinal cord that’s concerned with pain processing. And we know by its shape that it’s one of nerve terminals of a fiber that carries pain information. These are synapses of cells in the spinal cord. This is a neurotransmitter in little vesicles, and it’s black because it was reacted for an antibody to glutamate that was tagged with horseradish peroxidase, and then we did histochemistry on it to make that into an electron dense reaction product. This was evidence that, yes, these terminals are just filled with glutamate.
[Slide: “Glutamate Receptors”]
MR. WEINBERG: Ok, so that’s glutamate. Now what about glutamate receptors. We talked with glutamate as the presynaptic side, the axon bouton. What about the postsynaptic dendrite. Well, it turns out that after a lot of unsuccessful work, pharmacologists were finally able to make a variety of chemicals besides glutamate, that are sort of glutamate analogues that affect postsynaptic neurons in ways similar to glutamate. Two of these have the acronym AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-D-aspartate). I’m going to keep going back to AMPA and NMDA. Once they had these drugs, they were able to find other drugs called antagonists that would selectively block AMPA or selectively block NMDA. So if you had one of these AMPA antagonists, and you added AMPA, nothing happens. If you added NMDA antagonists, if you put an NMDA antagonist on and add NMDA, nothing happens. But if you put NMDA antagonists on and add AMPA, it works just fine. So they decided there must be NMDA and AMPA receptors.
[Slide]
MR. WEINBERG: Well, I thought they were silly, but what did I know. So, this is an electrical recording from a nerve cell. At its normal state of polarization, minus 60 millivolts, you stimulate a presynaptic axon that release glutamate and you get an excitatory potential called an EPSC [excitatory postsynaptic current]. Don’t worry about that. You put a special drug on that blocks NMDA receptors and what you get is this. And they say here is an AMPA component. You know it’s an AMPA component because if you then add to it a drug that blocks AMPA, this goes away and you get nothing. Contrariwise, here you have the same thing in EPSC. You put a drug on that blocks AMPA and your left with the NMDA component. So the whole thing is a combination of the NMDA and the AMPA component. The AMPA is fast. The NMDA is slower.
[Slide AMPA and NMDA diagrams]
MR. WEINBERG: In the last ten years, there have been a heck of a lot of work on this. They know a lot about these proteins now and there are good reasons for it. I’m not going to have time to tell you all of the reasons for it, but I’m going to hint at a few of the reasons. This is a diagram, a cartoon of an AMPA and NMDA receptor. This is the lipid by layer. This is inside. This is outside. This is where glutamate will be released and bind. This is glutamate binding to the receptor. When glutamate binds to the receptor that opens the channel, allowing current to flow which causes the EPSP [excitatory postsynaptic potential]. NMDA and AMPA, a little in particular, NMDA has more stuff in it, more things control it and regulate it, and it’s a little more complicated.
[Slide]
MR. WEINBERG: Well… Already? Gosh. Trouble, trouble, trouble. Ok, we wanted to know where these proteins were. Here we studied an AMPA receptor subunit using horseradish peroxidase. We were able to show that it was present in the dendrite, but that was about all we could say because the enzymatic reaction product diffuses some distance. You can’t get very good special resolution. This was using the same approach but using the immunogold label, which is much better localized. It’s these little black dots. So sure enough, the glutamate receptor is right at the postsynaptic membrane.
[Slide]
MR. WEINBERG: Now to look at this in a little more detail, this is the immunoglobulin that recognizes the substance. This is a gold particle. Because of the nature of the process, there is about a 20 nanometer range of possible error because where it ends up sitting down isn’t exactly where the sight of binding is. So there is maybe a little slop. Twenty nanometers is pretty good, but it’s not exact. So I had a post-doc, Victor Kerasia, who decided to take a look at this more systematically.
[Slide]
MR. WEINBERG: What he did was he just stained a lot of synapses in the cerebral cortex using immunogold for AMPA or NMDA subunits, and looked at where they were, and made a histogram of it. This is the distance to here. Ok. What he found was a spread, but that spread is about plus or minus 20 nanometers, which corresponds to the measurement error. So, if you don’t think about that measurement error, I mean if you try to correct for that and imagine what underlying distribution would give that, what you get is something that corresponds to right about here, which is just inside the plasma membrane. Ok. Just inside the plasma membrane. Moreover, though I don’t really claim that you can see it, the NMDA receptor is about two nanometers further than the AMPA receptor. That’s just barely statistically significant. Well, make sense? The answer is, ha, ha, it does.
[Slide]
MR. WEINBERG: This is a cartoon worked out by the molecular biologists of the protein organization of a subunit of an AMPA receptor. As all proteins, they are chains of amino acids. Amino acids have an N terminal and a C terminal. So a protein has an N terminal and a C terminal. Here is the N terminal. Here is the C terminal. This is outside. This is inside. Well, it turns out that the antibody that we were using recognizes the C terminal part of an AMPA receptor. So you would expect to see it just inside the membrane. And moreover, it turns out the NMDA receptor is organized just like the AMPA receptor except that it has a somewhat longer C terminus. So sure enough, you would expect to see it just a little bit further inside. So everything is as it should be.
[Slide: “Synaptic plasticity”]
MR. WEINBERG: And I have about three minutes to talk about the rest of the brain.
[Slide]
MR. WEINBERG: Let me zip through this and see if there is anything worth saying. Ok, the point is that besides the short transient phenomenon, there are also long term phenomenon that are important to the functioning of the brain. The fundamental thing to think about, although not the only example, is memory. While we don’t understand memory at any molecular level, an experimental tool that is being used recently that there has been great excitement over is synaptic plasticity. That is synapses can become more or less effective… Five minutes? Ok, yeah. And that’s been study particularly in the hippocampus, which is a region in this part of the brain that people know from different clinical and psychological studies, to be important for certain kinds of memory, particularly special memory. So when you get lost next time, you can just blame it on your hippocampus. Well, it turns out that you can actually cut a slice of hippocampus from the brain of a euthanatized rat and keep it alive for several hours in a petri dish…
[Slide]
MR. WEINBERG: …and that’s permitted very extensive study of this system, particularly this pathway, this synapse, where you stimulate the efferent fiber going to it and record from the nerve cell. This synapse releases glutamate, and the point to keep in mind here, is that if you stimulate once every five seconds, you get a certain synaptic potential, a certain amount of depolarization. It’s stable. It can be stable for hours, but if then, after you get a base line, 100 percent, you then deliver a rapid train of 100 stimuli over a period of a second, something changes. You get a whopping increase in the response. That increase settles down over five or ten minutes, but then it sticks around. It sticks around for an hour or more. If you do it right, it sticks around for a long time. You can’t keep these things alive in a dish forever, but there is good reason to think that you can do the same thing, pretty much, in a live animal and it will stay this way for weeks at least, if not forever. So people think that this might be one of the molecular, or one of the cellular substrates for things going on in memory.
[Slide]
MR. WEINBERG: Now what they think is happening is glutamate is being released all the time. Glutamate reacts at AMPA and NMDA receptors. But I tricked you. NMDA receptors, ha, ha, don’t normally work because they have magnesium ions in them that block its activity. It only unblocks when the thing is already depolarized by, for example, a train of stimuli that have activated AMPA receptors to cause a progressive depolarization. When this gets unblocked, the NMDA receptor starts working and allows a massive influx of calcium, and calcium, I told you at the beginning, acts on a whole bunch of different proteins, and these bunch of different proteins may cause biochemical changes that lead to long term reorganization of the synapse.
[Skips five slides]
MR. WEINBERG: This is a cartoon summarizing a lot of information from Eric Kandel’s textbook. He just won the Nobel Prize this year for pioneering work in synaptic plasticity in the hippocampus in an invertebrate. But it turns out there are mechanisms both operating on the postsynaptic side changing, for example, the concentration of postsynaptic receptors and mechanisms on the presynaptic side changing the efficacy of transmitter release.
[Skips slide]
MR. WEINBERG: I think I’ll have to stop there. I want to thank all my collaborators, the post-docs and students who have done the work for me, and my collaborators elsewhere. It sort of brings home to me one of the nice things about science, which is that you are sort of automatically part of a large community. What I’ve told you this evening is just a tiny little piece of this stuff that goes on with 25,000 people each year at the neuroscience meeting. And even if you took all of that stuff, you wouldn’t have a clue as to how the brain works because we don’t know how the brain works, but we are learning very, very slowly. Thank you for your time.
[Applause]
MR. WEINBERG: And I’ll take questions. Can we get the lights? So I’ll take questions from the audience now. No questions?
[Inaudible audience member]
MR. WEINBERG: Yeah. Neurons talk to each other. What do I mean by synaptic plasticity? What do I mean by synaptic plasticity? Neurons talk to each other via synapses. Ok, when an action potential, an action potential is completely stereotyped. When an action potential goes to a nerve terminal, the synapse turns on and you get a postsynaptic response. If you give 100 action potentials, you get 100 synaptic responses. Ordinarily, we think of that as stereotyped. The same action potential gives the same response, but it ain’t necessarily so. The synapse may become more effective. The synapse might become less effective. So they synapse has this property of plasticity. That is it changes for long periods of time to become more effective, or less effective.
[Inaudible audience member]
MR. WEINBERG: Normal magnetic fields, so far as people know, do things to the brain. It is possible… there are high tech methods that, I’m sure the people in the audience know better than I do, that can record magnetic fields in the brain as a result of the electrical activity of the neurons. There are some technical advantages to this although it requires very formidable machinery to do so. In addition to this, while a static magnetic field, as far as it is known, has no effect. A transient magnetic field induces I don’t know what, magnetic currents or something. Under the right circumstances that can actually stimulate a particular region of the brain causing various kinds of illusions, or so on, in an experimental subject.
[Inaudible audience member]
MR. WEINBERG: Yeah, the question is if understanding the brain is hopeless, what about neural nets? Can they tell us something about the brain? The short answer is yes, but first I need to qualify. We don’t understand the brain. We understand a little bit about the brain and we probably understand more each year. In my lifetime, there is no way we are going to understand what, to my mind, is a lot about the brain. Will we ever? I don’t know. Does modeling have something to tell us about how brains might work? Unquestionably, it does. At the same time, it has a bad reputation. It has a bad reputation because it promised too much too early. There were a lot of ambitious people who got excited about it. It’s understandably exciting. There was a divergence. What happened was that they got excited originally because they thought this might tell us how the brain works. Then it turned out they weren’t getting very far. They needed to keep the money flowing and they started to realize that if they weren’t getting very far in understanding how the brain works. They were doing pretty well in understanding how to use computers to do various useful kinds of things: language translations, or handling complicated problems with arranging scheduling for airlines, and things like that. So the electrical engineering field of neural networks has sort of taken on a very vital life of its own [inaudible] remains a very useful and important [inaudible] of realistic neural networks that have helped us to understand certain aspects of neural processing and will continue to in the future. But there is a limit to it. Some of the limit, again, is because it’s complicated. Some of it is sociological that, in fact, engineers and biologists [inaudible] each other as much as they should. Yeah.
AUDIENCE MEMBER: I wanted to ask you about something that confuses me very much.
MR. WEINBERG: Yes, sir.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
MR. WEINBERG: Yes.
[Inaudible audience member]
[Laughter]
MR. WEINBERG: Did I read his book? No. If I had read it, would I understand it? No. Is he a genius? Yes. Is he right? Probably to a very, very limited extent. He has, in my opinion…
[End Video 2]
[Begin Video 3]
MR. WEINBERG: …the problem that comes with being brilliant and winning a Nobel Prize, and that is it is hard to maintain perspective. So, I think he has something very important to say, but I think it’s not quite as important as he thinks, and I think he didn’t do a very good job of making it accessible. In the simple minded Mickey Mouse way that I understand it, it’s that neurons try different ways of understanding stuff, and there are a lot of neurons there. Ok, you got 10 billion neurons, each one has got 50,000 synapses, and they screw around with different stuff until they get something that sort of works. And if something sort of works, they go for it. Hey. At some level, that is probably true, but I don’t know why, but Francis Crick, who by rights should be accused of exactly the same, is exposed to exactly the same mediology as [inaudible] namely being a genius and winning a Nobel Prize, seems to have a much more feet-on-the-ground attitude about it. My speculation is that maybe [Gerald] Edelman, I think got his prize in biology and so he supposed that he already understood it. Whereas Crick, well Crick got his in biology, but he was a physicist, alright. So he must of on some level known he didn’t know what was going on. But I don’t know.
[Inaudible audience member]
MR. WEINBERG: Ok, there was a question back there.
AUDIENCE MEMBER: You mentioned that glutamate rich foods are mushrooms and tomatoes.
MR. WEINBERG: I’m not sure. I think so. Tomatoes I’m sure.
AUDIENCE MEMBER: They have always made me feel better. [Laughter] Should I continue having, keeping them on my diet?
MR. WEINBERG: I strongly recommend that you eat what makes you feel good. [Laughter] I’m sorry. Let me make an addition. Two principles of eating: eat what makes you feel good, and eat what tastes good. [Laughter]
AUDIENCE MEMBER: This is back to the question on synaptic plasticity.
MR. WEINBERG: Yeah.
AUDIENCE MEMBER: You made reference to changing magnetic fields…
MR. WEINBERG: Yeah.
AUDIENCE MEMBER: …along synaptic activity, or presumably alluding to the effect of hallucinations in some subjects. Has there been any speculation or study with regard to conceivably, as small as this is. Is there a change at the synaptic junction when there is movement, electrochemical movement, either through the neurons or across, particularly though the synaptic junction. Would it not be conceivable that there is coincident with that a brief magnetic field generated, which in turn could affect other synaptic processes? I don’t know how one would map something like this, but it seems like depending on the nature and the direction of the synaptic movement, this could in turn affect, you know, how other synapses are functioning. Has anyone looked into that at this point?
MR. WEINBERG: Ok, I can’t give a whole and full answer to that. I can give a sort of talk around it. One, there has been a lot of excitement about the possibility of electromagnetic fields doing something bad to the body. I don’t think anybody, today, really knows. But the bulk of the available, the bulk of the available epidemiological research today argues that its very little of a problem, if any, that might also possibly effect the brain, thought processes and so on. So far as I know, there is no evidence to support it, although it can’t be ruled out. Now, you’re talking more about another thing, I think, which is sort of direct electrical, electromagnetic influences from one neuron to another. If you take the non-crack component of ESP, of let’s say telepathy, I think that the people who have taken it seriously in the past, who were saying maybe you really can transmit thoughts, one of the things they considered was the possibility that there might be some kind of electromagnetic emanation. I think that there is a lot of reason to think that is not true. The biggest reason has to do with sort of physical arguments having to do with arguments of scale that just impress most people with the very implausible. I don’t think that the implausibility arguments, I think they are pretty good with ESP, but I don’t think they are so good with respect to one part of the brain versus a different part of the brain. Because what physicists don’t realize is that there are biological systems that are capable of detecting extraordinarily slight electric fields. Biological systems can make sensors that are about as good as physical sensors, but I guess what I would say is that, at this point, the general view is that it doesn’t amount to much. Yes, sir.
[Inaudible audience member]
MR. WEINBERG: That’s a big number. So if there is an effect, it will be an electromagnetic effect.
[Inaudible audience member]
MR. WEINBERG: Ok.
[Inaudible audience member]
MR. WEINBERG: Ok, so I was too harsh on Edelman. [Laughter] And I agree with you. I think that there is something incredibly irresponsible in my bad rapping some guy when I haven’t even had the time to sit down and read his book carefully. I’ve had some people that I respect tell me that he is really onto something. What I’m personally convinced of is that whether he is on to something or not, it’s not on “the key” to understanding the brain. And that I’ll bet on, whether he’s right or not about his neuro-Darwinism.
[Inaudible audience member]
MR. WEINBERG: I don’t… That’s exactly why I’ll bet on it because I don’t think there is a key. Maybe we should stop now and if people want to continue to ask questions I’ll stay here and answer questions until the cows come home, but why don’t we stop and let people who need to get home, go.
[Applause]
MR. WEINBERG: Thank you very much.
[End of Lecture]